It is desirable when disseminating digital compressed data to prevent unauthorised alteration of the compressed data. Copy protection and authentication techniques for addressing this undesirable behaviour include public/private key encryption and the use of hash generated digital signatures. Example non-alteration techniques using real-time labelling of digital video data are described in the paper “Real-time Labelling of MPEG-2 Compressed Video” by Gerrit C. Langelaar, Reginald L. Lagendijk and Jan Biemond of Delft University of Technology, The Netherlands.